/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Copyright (C) 2022-2025 OpenFOAM Foundation
     \\/     M anipulation  |
-------------------------------------------------------------------------------
License
    This file is part of OpenFOAM.

    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.

    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.

\*---------------------------------------------------------------------------*/

#include "multiphaseEuler.H"
#include "fvcSmooth.H"
#include "fvcSurfaceIntegrate.H"

// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //

void Foam::solvers::multiphaseEuler::setRDeltaT()
{
    volScalarField& rDeltaT = trDeltaT.ref();

    const dictionary& pimpleDict = pimple.dict();

    const scalar maxCo
    (
        pimpleDict.lookupOrDefault<scalar>("maxCo", 0.2)
    );

    const scalar rDeltaTSmoothingCoeff
    (
        pimpleDict.lookupOrDefault<scalar>("rDeltaTSmoothingCoeff", 0.02)
    );

    surfaceScalarField maxPhi("maxPhi", phi);

    forAll(movingPhases, movingPhasei)
    {
        maxPhi = max(maxPhi, mag(movingPhases[movingPhasei].phi()));
    }

    // Set the reciprocal time-step from the local Courant number
    rDeltaT.internalFieldRef() = fvc::surfaceSum(maxPhi)/((2*maxCo)*mesh.V());

    // Clip to user-defined maximum and minimum time-steps
    scalar minRDeltaT = gMin(rDeltaT.primitiveField());
    if (pimpleDict.found("maxDeltaT") || minRDeltaT < rootVSmall)
    {
        const scalar clipRDeltaT = 1/pimpleDict.lookup<scalar>("maxDeltaT");
        rDeltaT.max(clipRDeltaT);
        minRDeltaT = max(minRDeltaT, clipRDeltaT);
    }
    if (pimpleDict.found("minDeltaT"))
    {
        const scalar clipRDeltaT = 1/pimpleDict.lookup<scalar>("minDeltaT");
        rDeltaT.min(clipRDeltaT);
        minRDeltaT = min(minRDeltaT, clipRDeltaT);
    }

    Info<< "Flow time scale min/max = "
        << gMin(1/rDeltaT.primitiveField()) << ", " << 1/minRDeltaT << endl;

    // Update the boundary values of the reciprocal time-step
    rDeltaT.correctBoundaryConditions();

    fvc::smooth(rDeltaT, rDeltaTSmoothingCoeff);

    Info<< "Smoothed flow time scale min/max = "
        << gMin(1/rDeltaT.primitiveField())
        << ", " << gMax(1/rDeltaT.primitiveField()) << endl;

    if (faceMomentum)
    {
        if (!trDeltaTf.valid())
        {
            trDeltaTf = new surfaceScalarField
            (
                IOobject
                (
                    fv::localEulerDdt::rDeltaTfName,
                    runTime.name(),
                    mesh,
                    IOobject::READ_IF_PRESENT,
                    IOobject::AUTO_WRITE
                ),
                mesh,
                dimensionedScalar(dimless/dimTime, 1)
            );
        }

        trDeltaTf.ref() = fvc::interpolate(rDeltaT);
    }
}


// ************************************************************************* //
